ATSHA204A-XHCZ-T 查看數據表（PDF） - Microchip Technology
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ATSHA204A-XHCZ-T Datasheet PDF : 93 Pages
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ATSHA204A
Single-Wire Interface
5.3
5.3.1
5.3.2
Synchronization
Because the communications protocol is half-duplex, there is the possibility that the system and the
ATSHA204A can fall out of synchronization with each other. In order to speed recovery, the device
implements a timeout that forces it to sleep under certain circumstances.
I/O Timeout
After a leading transition for any data token has been received, the ATSHA204A expects the remaining
bits of the token to be properly received by the device within the tTIMEOUT interval. Failure to send enough
bits or the transmission of an illegal token (a low pulse exceeding tZLO) causes the device to enter the
sleep state after the tTIMEOUT interval.
The same timeout applies during the transmission of the command block. After the transmission of a legal
command flag, the I/O timeout circuitry is enabled until the last expected data bit is received.
Note: The Timeout Counter is reset after every legal token and the total time to transmit the command
may exceed the tTIMEOUT interval while the time between bits may not.
The I/O timeout circuitry is disabled when the device is busy executing a command.
Synchronization Procedures
If the device is not busy when the system sends a transmit flag, the device should respond within
tTURNAROUND. If tEXEC time has not already passed, the device may be busy and the system should poll or
wait until the maximum tEXEC time has elapsed. If the device still does not respond to a second transmit
flag within tTURNAROUND, it may be out of synchronization. At this point, the system may take the following
steps to reestablish communication:
1. Wait tTIMEOUT.
2. Send the transmit flag.
3. If the device responds within tTURNAROUND, then the system may proceed with more commands.
4. Send a Wake token.
5. Wait tWHI.
6. Send the transmit flag.
7. The device should respond with a 0x11 status within tTURNAROUND, at which time system may
proceed with commands.
Any command results in the I/O buffer may be lost when the system and device lose synchronization.
5.4 Sharing the Interface
Multiple CryptoAuthentication devices may share the same interface, as follows:
1. System issues a Wake token (Section Watchdog Failsafe) to wake-up all devices.
2. The system issues the Pause command to put all but one of the devices into idle mode. Only the
remaining device then sees any commands that the system sends. When the system has
completed talking to the one active device, it sends an idle flag, which the idle devices ignore, but
puts the single remaining active device into the idle mode. See Section Pause Command for more
details.
Steps 1 and 2 are repeated for each device on the wire. If the system has completed communications
with the final device, it should wake all the devices up and then put all the devices to sleep to reduce total
power consumption.
© 2018 Microchip Technology Inc.
DS40002025A-page 24
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